1. Field of the Invention
The present invention relates to a milk calcium composition obtained from milk and a method for producing the same.
The milk calcium composition of the present invention can be added to a drink or food product for calcium fortification since it is highly dispersible and tasty.
2. Description of the Related Art
Calcium intake by the Japanese is currently below the nutritional requirement of 650 mg a day, and this level is difficult to attain from the current average Japanese diet. Since the absorption rates of calcium varies by its origin, it is necessary to choose a form of calcium with a high absorption rate.
Calcium in milk is drawing attention because of its high absorption rate. In milk, 60 to 70% of the calcium is bound to casein, or is incorporated into casein micelles forming colloidal calcium. These forms are considered to make calcium highly utilizable in the body. However, the conventional isolation and purification of calcium from milk produce insoluble calcium phosphate, which causes a marked deterioration in its quality by inducing recoagulation or crystal growth when added to drinks or food products.
Therefore, various attempts have been made to develop calcium compositions which are derived from milk and which are highly dispersible. Examples of methods for producing such calcium compositions include a method in which milk or skimmed milk is acidified or treated with rennin to remove casein by coagulation and precipitation, the resultant whey or supernatant is filtered through a UF membrane, then the filtrate is recovered and neutralized to obtain a calcium component as a precipitate (Japanese Patent Publication No. 3-24191/1991); a method for producing calcium-fortified milk drinks, in which the proteins in whey or milk supernatant are removed by treating with an ion exchange resin, a UF membrane or the like, then the lactose is crystallized and the solution is neutralized and filtered through a UF membrane or microfiltration (MF) membrane (Japanese Patent Laid-open No. 9-23816/1997); a method for recovering milk minerals in which a supernatant prepared by acidification is filtered through a UF membrane, organic acids are added to the filtrate to adjust the pH below 3.0, then the filtrate is concentrated and lactose is removed (Japanese Patent Laid-open No. 60-232052/1985); a method for recovering milk minerals, in which whey or milk supernatant is adjusted to a pH of 3.5 to 8.5, then filtered through a UF membrane to obtain a filtrate, or whey or milk supenatural is filtered through a UF membrane after which the pH of the filtrate is adjusted to pH 3.0 to 8.5, then the resultant filtrate is concentrated and lactose is removed (Japanese Patent Laid-open No. 63-87944/1988; Japanese Patent Laid-open No. 63-87945/1988); a method for producing milk-derived calcium which is soluble at a pH lower than 4.6, in which whey or milk supernatant, or the filtrate obtained by filtering whey or milk supernatant through a membrane is concentrated by heating, then the lactose is removed (Japanese Patent Laid-open No. 3-83564/1991); and a method in which milk supernatant prepared by acidification is heated, then neutralized to form insoluble minerals (Japanese Patent Laid-open No. 59-34848/1994 and Japanese Patent Publication No. 2-60303/1990).
Although it is possible to recover milk-derived calcium using any of these methods, the calcium thus obtained is poorly soluble or dispersible and would precipitate when used in drinks or food products such as desserts, which causes deterioration in quality by inducing precipitation. Moreover, minerals, including calcium, partly precipitate by removing lactose, which decreases calcium recovery.
Examples of commercial calcium compositions derived from milk include LACTOVAL(trademark) (18.6% by weight calcium, 6.3% by weight proteins, a product of DMV) and ALAMIN(trademark) 995 (25% by weight calcium, 10.3% by weight proteins, a product of New Zealand Dairy Industry). However, aggregation of the calcium in these compositions is controlled by simple physical refining or emulsification such that calcium solubility is not necessarily improved. ALANATE(trademark) 385 (1.4% by weight calcium, 92% by weight proteins, a product of New Zealand Dairy Industry) is another commercial calcium composition derived from milk. However, this calcium composition is a calcium caseinate, which is produced by dispersing acid casein in water, then dissolving it with calcium hydroxide, such that the major protein component is casein, which results in an undesirable unique odor known as xe2x80x9ccasein odor.xe2x80x9d
In the course of an intensive study to resolve the above-mentioned problems in milk-derived calcium, the present inventor found that by maintaining the calcium-protein ratio and the calcium-sodium ratio in the composition in a certain range, a milk calcium composition which is highly dispersible and tasty could be obtained. The present invention was thus accomplished. Accordingly, among others, an objective of the present invention is to provide a milk calcium composition obtained from milk, which is highly dispersible and tasty, and a method for producing the same.
It is known that about 66% of calcium in milk is generally present in a form of colloidal calcium and bound to casein (Shu-ichi Uenokawa et al., editors, xe2x80x9cScience of Milk,xe2x80x9d p. 55, 1994, National Agricultural Cooperative Dairy Plant Association). In the present invention, milk is concentrated by filtering through a UF membrane to recover this casein-bound calcium in a high concentration. In LF-membrane filtration, calcium bound to proteins or casein cannot pass through the UF membrane while low molecular components such as lactose, minerals and amino acids pass through the LF membrane; thus, calcium can be recovered in a high concentration. The degree of concentration is preferably about 1.5-6.0 times for skimmed milk or partially skimmed milk. If less than 1.5, the concentration of calcium relative to total solids is low, which is not suitable for practical use. Conversely, a concentration more than 6.0 times is undesirable because the concentrated milk becomes highly viscous, which markedly decreases concentration efficiency. In order to further remove low molecular components other than calcium, desalting by LF-membrane filtration may be carried out while adding water. Such desalting increases the concentration of calcium relative to total solids. Also, reconstituted skimmed milk can be used in the same manner as skimmed milk or partially skimmed milk. A milk protein concentrate (MPC) having an increased protein content can also be used after reconstitution.
Next, the concentrated milk is subjected to acid treatment, and then the precipitated casein is removed to obtain whey.
The term xe2x80x9cacid treatmentxe2x80x9d as used in the present invention refers to a process to precipitate casein, in which the pH is adjusted to 3.0 to 5.6 to precipitate casein by adding an inorganic acid such as hydrochloric acid, sulfuric acid, phosphoric acid and boric acid, or an organic acid such as acetic acid, lactic acid, gluconic acid and malic acid, or by inoculating lactic acid bacteria for lactic acid fermentation. In particular, the use of acids having a high chelating activity, such as citric acid, can increase the calcium concentration in whey because these acids can separate casein-bound calcium intensively. Further, higher calcium recovery can be attained by adding the wash obtained from casein by washing the precipitated casein with water to the whey.
In order to effectively utilize milk components, if necessary, those components such as lactose and minerals removed in the UF-membrane filtration can be added to the whey, and its solid content is adjusted, then the pH of the whey is adjusted preferably to 6.0 to 9.0. The milk calcium composition is poorly dispersed and less tasty if the pH of the whey is below 6.0. A whey pH of higher than 9.0 is not desirable because it fouls the taste of the milk calcium composition.
For the pH adjustment, alkaline solutions, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, magnesium hydroxide, and sodium citrate can be used.
The whey is then concentrated by filtering through a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane, or by concentrating under vacuum to obtain a milk calcium composition. An NF membrane is preferably used for the concentration of the whey, because the NF membrane allows monovalent salts such as sodium to filter through, but concentrates divalent salts such as calcium, wherein calcium can be effectively concentrated. In order to further increase the calcium concentration in the milk calcium composition, desalting by filtration with an NF membrane, or electrodialysis followed by concentration by RO membrane filtration or under vacuum can be carried out.
The concentrate thus obtained can be used as a milk calcium composition without further processing. Also, this concentrate can be frozen to produce a frozen product, or spray-dried or freeze-dried to produce a powdered product to be used as a milk calcium composition.
This milk calcium composition contains components in the following ratios (1) and (2) and is highly dispersible and tasty.
(1) xe2x88x921.3xe2x89xa6log{(% by weight calcium in composition)/(% by weight protein in composition)}xe2x89xa60.26
(2) 0.9xe2x89xa6log{(% by weight calcium in composition)/(% by weight sodium in composition)}.
The reason that the milk calcium composition of the present invention is highly dispersible and tasty is because aggregation among calcium and the growth of calcium crystals are controlled by the presence of a certain amount of whey proteins, and the content of salts, such as sodium, which affects the taste, are reduced to a certain level. Thus, a milk calcium composition of practical use can be provided.
If the value of log{(% by weight calcium in composition)/(% by weight protein in composition)} for the milk calcium composition is smaller than xe2x88x921.3, the calcium content relative to milk solid is low, and thus the composition has no practical value. If the value of log{(% by weight calcium in composition)/(% by weight protein in composition)} for the milk calcium composition exceeds 0.26, the calcium is poorly dispersible. If the value of log{(% by weight calcium in composition)/(% by weight sodium in composition)} for the milk calcium composition is smaller than 0.9, the undesirable taste resulting from salts, such as sodium, is intensified.